In recent years, studies on flexible devices having flexibility and stretchability have been actively conducted (ex. Mallory L. Hammock et al., “25th Anniversary Article: The Evolution of ElectronicSkin (E-Skin): A Brief History, Design Considerations, and Recent Progress,” Advanced Materials, vol. 25, pp. 5997-6038, 2013). Further, as wires to be used in the flexible devices, there are known wires made of conductive elastomer materials, and metal wires having curved shapes (ex. Tsuyoshi Sekitani et al., “Stretchable active-matrix organic light-emitting diode display using printable elastic conductors,” Nature Materials, vol. 8, pp. 494-499, 2009, and Darren S. Gray et al., “High-Conductivity Elastomeric Electronics,” Advanced Materials, No. 5, pp. 393-397, 2004). However, there are problems in that the conductive elastomer has low conductivity, and the curved metal wires may be cracked by stretching.
Specifically, as a stretchable wire that has been studied so far, conductive rubber obtained by mixing a conductive material into a rubber material or a gel material is most popular, but its electric conductivity is about 101 S/m. Further, even a gel material reported in the Sekitani et al., which is said to have significantly higher conductivity than that of the related art, has a resistance to stretching of 29% and conductivity of only 1.02×104 S/m. Those values of conductivity are significantly lower than that of gold (Au) used as a solid wire material, which is 4.6×107 S/m.
Meanwhile, as a stretchable wire using metal, a metal wire is formed into a zig-zag shape, to thereby achieve a device that does not disconnect even when stretching occurs to some extent (ex. Dae-Hyeong Kim et al., “Epidermal Electronics,” Science, vol. 333, pp. 838-843, 2011). However, metal is only used, and hence not only the stretchability is limited, but also there is a fear of fatigue failure due to repeated stretching. Usage of metal is preferred as the stretchable wire in consideration of high conductivity, but, so far, there are no reports that have used metal and achieved high resistance to stretching (that is, no disconnection due to stretching or no fatigue failure due to repeated stretching).
Further, as a study example of a self-healing wire when a crack is generated in a metal wire, there has been reported a study involving forming a wire by injecting solder into a flow channel of silicone rubber, and, when the wire is disconnected by deformation, applying heat to heal the disconnection (ex. A. C. Siegel et al., “Microsolidics: Fabrication of Three-Dimensional Metallic Microstructures in Poly(Dimethylsiloxane),” Advanced Materials, vol. 19, pp. 727-733, 2007). However, a combination of solid solder and a metal wire, which is a solid as well, requires heating up to a temperature capable of melting the solder, for example, every time the crack is healed. Thus, fundamental structural improvements of a crack healing portion have been demanded.